AVAudioMixInputParametersMBS class

Function:
An AVAudioMixInputParameters object represents the parameters that should be applied to an audio track when it is added to a mix. Notes:
Audio volume is currently supported as a time-varying parameter. AVAudioMixInputParameters has a mutable subclass, AVMutableAudioMixInputParameters.

You use an instance AVAudioMixInputParameters to apply audio volume ramps for an input to an audio mix. Mix parameters are associated with audio tracks via the trackID property.

Before the first time at which a volume is set, a volume of 1.0 used; after the last time for which a volume has been set, the last volume is used. Within the time range of a volume ramp, the volume is interpolated between the start volume and end volume of the ramp. For example, setting the volume to 1.0 at time 0 and also setting a volume ramp from a volume of 0.5 to 0.2 with a timeRange of [4.0, 5.0] results in an audio volume parameters that hold the volume constant at 1.0 from 0.0 sec to 4.0 sec, then cause it to jump to 0.5 and descend to 0.2 from 4.0 sec to 9.0 sec, holding constant at 0.2 thereafter.